DESCRIPTION (Applicant's abstract): The objective of this project is to identify the mechanisms contributing to orthostatic intolerance in the heat. This objective will be accomplished by comparing the effects of normothermia versus whole-body heating on hemodynamic factors relating to orthostatic tolerance, on cerebrovascular autoregulation, on presynaptic control of sudomotor and vasomotor function, and adrenoceptor-mediated cutaneous vasoconstriction. This integrated research approach will be able to identify potential mechanisms leading to orthostatic intolerance in the heat.